The invention relates to vehicle navigation apparatus.
Vehicle navigation systems can be divided into two types, one that holds route information locally in the vehicle, and another in which the vehicle accesses a remote data base providing route information.
The second type of system has advantages. Whereas locally held information will become out of date and need to be up dated by each user at the respective local station, a central data base can be continually updated. A user will, accordingly have up-to-date information whenever it is required. Additionally a system in which route information is held locally must store all the information a user is likely to require. This is expensive in terms of memory and also route calculation time. In central information system, the user needs only send start and endpoint information and receive a suggested route from the central database. This requires less memory storage capacity, and is more versatile as route information can be kept current on a daily, hourly, or on a more frequent basis.
Centrally determined route guidance (CDRG) which only yields an optimal path suffers from a lack of route alternatives once the driver leaves the optimal path. If this happens accidentally the driver would like to have a recovery option, either a newly planned route or a return to the previously determined route. A quick corrective response of the route guidance system is often necessary which could be difficult for the optimal path CDRG due to latency in the planning time.
Problems occur with receiving route information from a central database when a driver deviates from the provided route. This could be accidental as a result of a navigation error or necessary because of an unforeseen route blockage. If a large region surrounding the suggested route is mapped, there is more tolerance to driving errors but there is also likely to be additional cost to the user in terms of terminal memory.
Current systems usually rely on local CD-ROM based route guidance software and are sold by several vendors (Bosch/Blaupunkt, Philips, Alpine, Siemens, Delco, Marelli). They are autonomous in the sense that they do not have to contact a service provider. But the CD_ROM database gradually becomes obsolete and usually contains too much information to the user and also indicates alternative routes.